1. Field of the Invention
This invention relates to a data recording device using a video tape recording device, and more particularly, a data recording device in which data can be recorded at an optional speed.
2. Description of the Prior Art
In a usual helical scanning magnetic tape recording and reproducing device such as a VTR or the like, a recording is carried out at a specified normal speed during its recording operation. Further, in the case that a reproducing operation is carried out, a dynamic tracking technology or the like is applied to enable a noiseless reproduction to be realized from a stand-still state to a speed of several times of a normal speed.
In the general type of VTR, it is assumed that an amount of data per unit time of an image signal (30 frames in one second) is kept constant and the data is continuously processed without the need to record the data at a special tape speed.
As an exceptional case of a monitoring (surveying) VTR, an input image signal is recorded in drawing out data like one in which only one frame is left in an interval of 1 second, for example. In addition, an optional speed recording VTR enabling a frame-based photographing and a slow-speed recording to be carried out or a super-motion VTR capable of recording three times a normal input image signal are already products in the market.
However, in no case, have the existing VTRs realized a function to record all the data in a tape without dropping data inputted at an optional speed including an intermittent input.
Further, in order to fulfill a requirement for a recording operation at more optional speeds, there has been provided a stepless preset speed (provided that once starting the recording operation, no changing of the speed can be performed) and a product such as a variable rate buffer or the like has also been manufactured as a device for handling data in a continuous manner.
When it is assumed that a data recording is carried out as an external memory for a computer, for example, the magnetic tape recording and reproducing device with a helical scanning recording by a rotary head has a longer ready-running period, shows a more hard continuous data processing as compared with that of a longitudinal recording in parallel with a tape running direction in the prior art, and so this type of system has been improper for a data recording operation. However, as an amount of data has been remarkably increased due to an advancement of a processing capability of a computer in recent years, either a high speed helical scanning recording or a high recording density has been noticed and the magnetic tape data recording and reproducing device with the helical scanning recording has been put in the market as a product irrespective of the aforesaid disadvantages.
The usual magnetic tape recording and reproducing device of helical scanning has a disadvantage that a time ranging from a completion of recording to a subsequent continuous recording (stop-start time), i.e. a tape running time from an editing-out time in VTR to a tape stopping, pre-rolling, tape ready-running and an editing-in point (this is adjacent to an editing out point) is long.
The variable rate buffer stores all the inputted data once on a memory irrespective of the fact that this stop start time (no data can be recorded in the tape during this period) is present or the recording is being carried out and when a sufficient amount of data is accumulated, it transfers data in the memory to the tape at a normal speed recording. Then, the recording with respect to the tape is stopped concurrently with a vacant state of the data in the memory and then an operation waiting for the time in which sufficient data is accumulated on the memory is repeated.
In this way, the memory is used as a data buffer, a recording stop/start of the helical scanning magnetic tape recording and reproducing device is controlled concurrently with an on/off control of reading-out operation from the memory to realize a function to cause all the data inputted at an optional speed including an intermittent input to be recorded on a tape without any loss at all.
However, this method requires a semiconductor memory having a large capacity acting as a buffer corresponding to a minimum stop and start time. For example, if it is assumed that the stop/start time is 5 seconds and an inputting data speed is 32 MB/sec, a high speed RAM corresponding to 160 MB is required, resulting in that some severe disadvantages of 1) expensive in price and 2) data loss under a power failure becomes large.
As described above, in order to perform a data recording under a variable rate at the prior art data recording device, a certain degree of data loss is estimated or a memory of corresponding amount for the data to be recorded once on a memory is required, and in the former case, a problem of the data loss and in the latter case, its price or data loss under a power failure has been as a problem.
In view of the foregoing, it is an object of the present invention to realize the data recording device capable of recording data at an optional speed without any data loss by applying a buffer of memory capacity remarkably less than the memory capacity required in the prior art